text: Hinduism identifies six Pramāṇas as epistemically reliable means to accurate knowledge and to truths: Pratyakṣa (perception), Anumāna (inference), Śabda or āgama "(word, testimony of past or present reliable experts), Upamāna (comparison and analogy), Arthāpatti (postulation, derivation from circumstances), and Anupalabdhi (non-perception, negative/cognitive proof). Of these  epistemology considered only pratyakṣa (perception) and  (inference) as reliable means of valid knowledge. Yoga accepts the first three of these six as pramāṇa; and the Nyaya school, related to Vaiśeṣika, accepts the first four out of these six.
  * Pratyakṣa (प्रत्यक्ष) means perception. It is of two types: external and internal. External perception is described as that arising from the interaction of five senses and worldly objects, while internal perception is described by this school as that of inner sense, the mind. The ancient and medieval texts of Hinduism identify four requirements for correct perception: Indriyarthasannikarsa (direct experience by ones sensory organ(s) with the object, whatever is being studied), Avyapadesya (non-verbal; correct perception is not through hearsay, according to ancient Indian scholars, where ones sensory organ relies on accepting or rejecting someone elses perception), Avyabhicara (does not wander; correct perception does not change, nor is it the result of deception because ones sensory organ or means of observation is drifting, defective, suspect) and Vyavasayatmaka (definite; correct perception excludes judgments of doubt, either because of ones failure to observe all the details, or because one is mixing inference with observation and observing what one wants to observe, or not observing what one does not want to observe). Some ancient scholars proposed "unusual perception" as pramāṇa and called it internal perception, a proposal contested by other Indian scholars. The internal perception concepts included pratibha (intuition), samanyalaksanapratyaksa (a form of induction from perceived specifics to a universal), and jnanalaksanapratyaksa (a form of perception of prior processes and previous states of a topic of study by observing its current state). Further, the texts considered and refined rules of accepting uncertain knowledge from Pratyakṣa-pranama, so as to contrast nirnaya (definite judgment, conclusion) from anadhyavasaya' (indefinite judgment).
  * Anumāna (अनुमान) means inference. It is described as reaching a new conclusion and truth from one or more observations and previous truths by applying reason. Observing smoke and inferring fire is an example of Anumana. In all except one Hindu philosophies, this is a valid and useful means to knowledge. The method of inference is explained by Indian texts as consisting of three parts: pratijna (hypothesis), hetu (a reason), and drshtanta (examples). The hypothesis must further be broken down into two parts, state the ancient Indian scholars: sadhya (that idea which needs to proven or disproven) and paksha (the object on which the sadhya is predicated). The inference is conditionally true if sapaksha (positive examples as evidence) are present, and if vipaksha (negative examples as counter-evidence) are absent. For rigor, the Indian philosophies also state further epistemic steps. For example, they demand Vyapti - the requirement that the hetu (reason) must necessarily and separately account for the inference in "all" cases, in both sapaksha and vipaksha. A conditionally proven hypothesis is called a nigamana (conclusion).